Field of the Invention
The present invention relates to a wafer processing method by which a wafer having a plurality of division lines formed in a grid pattern on a front side thereof and having devices formed in a plurality of regions partitioned by the division lines is divided along the division lines.
Description of the Related Art
In a semiconductor device manufacturing process, a plurality of regions are partitioned by division lines arranged in a grid pattern on the front side of a semiconductor wafer having a substantially circular disk-like shape, and devices such as ICs and LSIs are formed in the thus partitioned regions. The thus formed semiconductor wafer is cut up along the division lines to divide the regions in which the devices are formed, thereby producing the individual device chips.
The cutting of the semiconductor wafer along the division lines as above is ordinarily conducted by use of a cutting apparatus called dicing saw. The cutting apparatus includes a chuck table for holding a workpiece such as a semiconductor wafer or an optical device wafer, cutting means for cutting the workpiece held on the chuck table, and feeding means for relatively moving the chuck table and the cutting means. The cutting means includes a spindle unit which includes a rotary spindle, a cutting blade mounted to the rotary spindle, and a driving mechanism for rotationally driving the rotary spindle. The cutting blade includes a circular disk-shaped base, and an annular cutting edge attached to a side surface peripheral portion of the base. The cutting edge is formed, for example, by fixing diamond abrasive grains with a grain diameter of about 3 μm to the base in a thickness of about 20 μm by electroforming.
Since the cutting blade has a thickness of about 20 μm, however, the division lines for partitioning the devices are required to have a width of about 50 μm, so that the ratio of the area of the division lines to the area of the wafer is high, which leads to a low productivity.
On the other hand, in recent years, as a method for dividing a wafer such as a semiconductor wafer, a laser processing method called internal processing has been put to practical use in which a pulsed laser beam having such a wavelength as to be transmitted through the wafer is applied to the wafer, with its focal point positioned in the inside of a region to be divided. The dividing method using the laser processing method called internal processing is a technology wherein the pulsed laser beam having such a wavelength as to be transmitted through the wafer is applied from one side of the wafer, with its focal point positioned in the inside of the wafer, so as to continuously form a modified layer in the inside of the wafer along each of division lines, and an external force is applied to the wafer along the division lines where wafer strength has been lowered due to the formation of the modified layers, thereby cracking and dividing the wafer along the division lines (see, for example, Japanese Patent Laid-Open No. 2004-160493).
As a method for dividing a wafer into individual devices by applying an external force to the wafer along the division lines of the wafer formed with the modified layers along the division lines in the aforementioned manner, a technology has been disclosed in Japanese Patent Laid-Open No. 2005-223282. In this technology, the wafer formed with the modified layers along the division lines is adhered to a dicing tape attached to an annular frame, and the dicing tape is expanded to apply a tension to the wafer, thereby dividing the wafer along the division lines where wafer strength has been lowered due to the formation of the modified layers, into the individual device chips.
In addition, Japanese Patent Laid-Open No. 2013-165229 discloses a technology wherein a protective tape is adhered to the front side of a wafer formed continuously with a modified layer along each of division lines, the protective tape side of the wafer is held onto a chuck table, thereafter the back side of the wafer is ground while supplying grinding water to thin the wafer to a predetermined thickness and divide the wafer into the individual device chips.